Ozone concentration sensor

ABSTRACT

An apparatus and method provide measurement of a constituent of a fluid, such as ozone in ozonated water. The apparatus includes a vessel to contain the fluid, a light source configured to direct a first band of light and a second band of light along a substantially shared path though the fluid, and a photosensor that senses the first band of light and the second band of light. The constituent has a greater absorption associated with the first band of light than with the second band of light. The method includes modification of a measured attribute of the component in response to the sensed second band of light to improve the accuracy of the measured attribute.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/397,155 filed Mar. 3, 2009, which is a continuation of U.S.patent application Ser. No. 10/799,331 filed Mar. 12, 2004, now U.S.Pat. No. 7,502,114, the disclosures of which are incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus and methods formaterials analysis. More particularly, the invention relates tomeasurement of ozone concentration of ozonated fluid.

BACKGROUND OF THE INVENTION

Ozone concentration in ozonated water is often measured via absorptionspectroscopy. Ultraviolet (UV) and yellow-red bands of light aresuitable due to a good match to ozone's absorption characteristics. Thepeak absorption for the UV Hartley band is about 2000 times greater thanfor the yellow-red Chappius band, so use of a UV source can providegreater measurement sensitivity than use of a yellow-red source. A UVsource, however, can be expensive and can produce an unstable lightintensity. Therefore, use of visible light can be preferred when thegreatest sensitivity is not required.

Ozonated water has many industrial applications. In the semiconductormanufacturing industry, for example, accurate control of the ozoneconcentration of ozonated water produced by an ozonated water generatorcan be critical during device fabrication. Common approaches tomeasuring ozone concentration for such generators are often slow, proneto error, and/or inconvenient. For example, ozone concentration can bemeasured by collecting a sample of ozonated water from the generator andtesting it with an absorption spectroscopy-based analytical device.Thus, there can be errors and delays in measurements due to samplehandling. Further errors can be introduced by anomalous scattering oflight as it passes through the water. Such scattering caused, forexample, by bubbles, can produce light intensity losses that can bedifficult to distinguish from intensity losses that are due to ozoneabsorption.

SUMMARY OF THE INVENTION

The invention involves an apparatus and methods that can improvemeasurement accuracy, ease, and cost for absorption spectroscopy ofattributes of a constituent of a fluid. According to principles of theinvention, measurement accuracy can be improved by correcting forintensity losses arising from effects other than constituent-absorptioneffects. The invention arises, in part, from the realization thatanomalous absorption can be determined by observing a second radiationthat travels a shared path with the first radiation and is less absorbedthan the first radiation. Measurement of the intensity of the secondradiation can thus be used to assess how much loss of the firstradiation is due to anomalous effects, such as scattering of theradiation by bubbles in the fluid.

The invention also arises, in part, from the realization that an outputpipeline of an ozonated water generator can be modified to permitfull-flow real-time (or near real-time) in situ measurements of ozoneconcentration. As described above, two bands of light, i.e., radiation,can be directed through a portion of the output pipeline, usingreflections, as desired, to increase a path length and thereby ameasurement sensitivity. The bands of light have different absorptioncharacteristics with respect to ozone; the band having lesser or noabsorption due to ozone provides a reference signal. By directing thetwo bands of light along substantially the same path, the referencesignal can be used to correct for intensity loss of the first band oflight arising from factors other than absorption by ozone.

The two bands of light can be provided, for example, by a yellow-lightlight-emitting diode (LED) and a blue-light LED. One or more LEDs canprovide a stable, low-cost source of light. Thus, ozone concentrationcan be measured by direct examination of the full-flow ozonated wateroutput of a generator in real-time with improved accuracy and lower costthan some prior methods.

Accordingly, in a first aspect, the invention features an apparatus formeasuring a constituent of a fluid, for example, ozone in ozonatedwater. The apparatus can include a vessel to contain the fluid, a lightsource configured to direct a first band of light and a second band oflight along a substantially shared path though the fluid, and aphotosensor.

The first band of light and the second band of light are selected sothat the absorption by the constituent of the first band of light isgreater than the absorption by the constituent of the second band oflight. The second band of light provides a reference signal to permitcorrection of measurements derived from the first band of light.

The photosensor senses the first band of light and the second band. Thephotosensor can include one or more components, for example, one or morephotodiodes. The photosensor supports intensity measurements of thebands of light. The measured intensity of the first band can provide adetermination of an attribute of the constituent, such as theconcentration of the constituent. The measured intensity of the secondband can provide a reference signal to support error corrections of theattribute determinations.

For example, the fluid can be water and the constituent can be ozone.The vessel can be, for example, a portion of a ozonated water deliverypipeline. Thus the apparatus can provide in situ measurement of ozoneconcentration in ozonated water as it flows from an ozonated watergenerator. An ozonated water generator can include the vessel as aportion of the generator's ozonated water delivery pipeline. Thus, theapparatus can support real-time measurements of ozonated water producedby the generator, without requiring collection of an ozonated watersample from the generator.

The component of the photosensor has an absorption band that overlapsthe first band of light. For example, for ozonated water measurements,the first band of light can be associated with a yellow-red frequencyand a first width, and the second band of light can be associated with ablue frequency and a second width. The blue light is relativelyunabsorbed by ozone. The light source can include one or more LEDs, forexample, a GaAsP on GaP LED.

The substantially shared path can be defined in part by at least onereflection site to increase a length of the path through the fluid inthe vessel, thereby increasing a measurement sensitivity for theconstituent in the fluid. A vessel having a compact size can thusprovide a relatively long path length.

Factors other than constituent absorption can cause a loss in intensityof the first and second bands of light passing through the fluid (suchfactors include, for example, bubbles in the fluid.) Thus, an observedloss of intensity of the second band of light provides an indication ofa loss of intensity of the first band of light that arises from suchfactors. Preferably, the paths of the first and second bands of lightare substantially shared so that the two bands of light pass throughsubstantially the same fluid. Thus, the second band of light can passthrough substantially the same fluid as the first band of light and/orsample substantially the same mechanical factor(s) as the first band oflight.

The vessel can include transparent, translucent, and/or opaquematerials. The apparatus can also include a coating adjacent to thevessel. The vessel itself can provide a reflection site. Alternatively,the coating can reflect the light. The reflection site can produce amirror or a diffuse reflection, depending upon the selection ofmaterials for the vessel and/or the coating.

The apparatus can include a second photosensor. The second photosensorcan support, for example, detection of differential aging effects of alight source that includes two LEDs. The apparatus can also include atemperature sensor and/or a pressure sensor. Temperature and pressuremeasurements can support further corrections to attributes determinedfrom intensity losses of the first band of light.

In a second aspect, the invention features a method for measuring aconstituent of a fluid, according to principles of the invention. Themethod includes selecting a first band of light for which theconstituent has a greater absorption than for a second band of light,sensing the first band of light and the second band of light passingalong a substantially shared path through the fluid, and modifying ameasured attribute of the constituent determined from the sensed firstband of light in response to the sensed second band of light to improvethe accuracy of the measured attribute.

The measured attribute of the ozone can be any attribute of interest,for example, a concentration of the ozone. The measured attribute can bemodified to correct the measured concentration for errors arising froman intensity loss of the sensed first band of light associated with oneor more factors other than absorption by the constituent (i.e., otherthan by absorption by ozone). Such intensity losses may otherwise bemisinterpreted as arising from absorption by ozone, and can thus lead toa false increase in measured concentration.

Factors that may cause a decrease in intensity include, for example,bubbles, a reflectivity of a reflection site of the substantially sharedpath, an impurity in the fluid, and a mechanical dimension of a vesselcontaining the fluid. For example, a change in reflectivity and/ordimensions of the vessel can cause a decrease (or increase) in ameasured intensity of the first band of light. Such a decrease (orincrease) in intensity is unrelated to absorption by ozone, but can befalsely interpreted as an increase (or decrease) in absorption by ozone.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described with particularity in the appended claims.The above and further advantages of this invention may be betterunderstood by referring to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram of an embodiment of an apparatus for measuringa constituent of a fluid, according to principles of the invention; and

FIG. 2 is a flowchart of an embodiment of a method for measuring acomponent of a fluid, according to principles of the invention.

DETAILED DESCRIPTION

Definitions—An “ozonated water generator” is an apparatus that producesozonated water by introducing ozone gas into water through use of, forexample, a contactor.

The term “light” refers to electromagnetic radiation, includinginfrared, visible, ultraviolet, and x-ray radiation. The terms “light”and “radiation” are herein used interchangeably.

A “band of light” is associated with a peak frequency and a bandwidth,for example, a half-maximum bandwidth.

A “vessel” is a container or portion of a container that can contain afluid. A vessel can be, for example, a pipeline or a portion of apipeline.

FIG. 1 is a diagram of a cross-section of an embodiment of an apparatus100 for measuring a constituent of a fluid, according to principles ofthe invention. The apparatus includes a vessel 110 to contain the fluid,a light source 120 configured to direct a first band of light and asecond band of light along a substantially shared path though the fluidin the vessel, and a photosensor 130 that senses the first band of lightand the second band of light passing along the substantially sharedpath. The first and second bands of light from light source 120 can betransmitted sequentially or simultaneously. For example, the first bandof light can be transmitted and detected by photosensor 130, and thenthe second band of light can be transmitted and detected by photosensor130. In other embodiments, the first and second bands of light can betransmitted simultaneously by light source 120. Detection of these bandsof light by the photosensor 130 can then be performed simultaneously.Embodiments also include sequential detection of the light bands byphotosensor 130 when both are simultaneously transmitted by light source120.

The first band of light and the second band of light are selected sothat the constituent to be measured has a greater absorption for thefirst band of light than for the second band of light. The second bandof light provides a reference signal to correct measurements derivedfrom the first band of light.

For example, the fluid can be water and the constituent can be ozone.The vessel 110 can then be, for example, a portion of a deliverypipeline for ozonated water to permit in situ measurement of the ozone.Thus, an ozonated water generator can be modified by using the vessel110 as a portion of a delivery pipeline of the ozonated water generator.The apparatus 100 can provide real-time, or near real-time, measurementsof ozonated water produced by the generator, without requiringcollection of an ozonated water sample from the generator.

The constituent to be measured has an absorption band that overlaps thefirst band of light. For example, for ozonated water measurements, thefirst band of light can be associated with a yellow-red frequency and afirst width, and the second band of light can be associated with a bluefrequency and a second width. The yellow-red frequency can be, forexample, approximately 584 nm, and the blue frequency can be, forexample, approximately 300 nm. The light source 120 can then include ayellow-red LED 120 a to provide the first band of light, and a blue LED120 b to provide the second band of light.

The yellow-red LED 120 a, for example, can be a GaAsP-on-GaP diode. Theyellow-red peak wavelength output of such a diode is close to ozone'smaximum absorption for visible light. Moreover, the associated ozoneabsorption band is broader than the width of the yellow-red output ofthe diode.

The substantially shared path can be defined in part by at least onereflection site A to increase a length of the path through the fluid inthe vessel. The measurement sensitivity of the apparatus 100 can beincreased by increasing the path length through the fluid.

The paths of the first and second bands of light are preferablysubstantially shared so that the two bands of light pass throughsubstantially the same fluid. As further described below, an observedchange in intensity of the second band of light can then provide a goodindication of the effect of non-constituent-related factors that haveaffected the intensity of the observed first band of light.

The vessel 110 can include transparent, translucent, and/or opaquematerials. Suitable materials include, for example, quartz, a resin,and/or a fluoropolymer such as polytetrafluoroethylene (PTFE) andperfluoroalkoxy (PFA). The apparatus 100 can also include a coating 150adjacent to the vessel. The vessel 110 itself can provide a reflectionsite for the bands of light. Alternatively, the coating 150 can reflectthe light.

The reflection site A can produce a mirror or a diffuse reflectiondepending on the selection of materials for the vessel and/or thecoating 150. For example, a white polymer vessel 110, or a clear quartzvessel 110 with a white paper coating 150, can provide a diffusereflection. Use of reflection sites A that produce a diffuse reflectioncan simplify design and manufacture of the apparatus 100 by reducing oreliminating a need to align reflection sites A of a mirror type. Thevessel 110 can thus include a material that defines an inner surface ofthe vessel that diffusely scatters the first and second bands of lightat the reflection site A. Alternatively, light may be allowed to passthrough a transparent vessel and to reflect from a coating 150.

The photosensor 130 senses the first band of light and the second bandof light passing along the substantially shared path. The photosensor130 can include, for example, one or more silicon photodiodes, phototransisitors, photo-multiplier tubes, or other devices known in the art.As described below, the photosensor 130 supports intensity measurementsof the bands of light. One photosensor (e.g., 130) can support more thanone component. For example, a photosensor can include two components,and each component can be a photodiode. A photosensor including twophotodiodes can simultaneously measure the intensities of two differentlight bands. The measured intensity of the first band can provide adetermination of an attribute, such as concentration, of a constituentin the fluid. The measured intensity of the second band can provide areference signal to support error corrections of the attributedeterminations.

The apparatus 100 can further include a second photosensor 140. Thesecond photosensor 140 can be positioned to sense the first band oflight and the second band of light after they pass along at most aportion of the substantially shared path. The second photosensor 140 canbe used to support detection of differential aging of, for example, theLEDs 120 a, 120 b. Thus, for example, a loss of light output from theyellow-red LED 120 a due to aging can be determined, and corrected, byincreasing a current supplied to the LED 120 a to increase its output.

In some embodiments, the first and second bands of light from lightsource 120 can be transmitted sequentially or simultaneously. If theyare transmitted simultaneously, then detection of either of these bandsof light by the second photosensor 140 can be performed simultaneouslyor sequentially. For example, one band of light can be detected byphotosensor 130, while the other band of light is simultaneouslydetected by the second photosensor 140.

Further, although only two bands of light have been described, more thantwo bands can be used. If more than two bands of light are transmittedby light source 120, at least one of photosensors 130, 140 can be usedto simultaneously detect two (or more) light bands of interest.Sequential detection can also be performed, either simultaneously (e.g.,with two photosensors) or sequentially (using one or two photosensors).

Based on this description, other suitable combinations will also becomeapparent to one of skill in the art. For example, other light sourceconfigurations can be used. A single light source can be used that hasan adjustable light wavelength output, which can be either continuouslyor discretely adjustable. The light absorption of the differentwavelengths could then be detected with photosensors as described above.Yet another embodiment includes multiple light sources and multipledetectors, in which each detector has a spectral sensitivitycorresponding to a particular one of the light sources. Thus, a firstlight source (e.g., a first photodiode) transmits a first light band andis paired with a first detector, a second light source (e.g., a secondphotodiode) transmits a second light band and can be paired with asecond detector, etc. Preferably, the light paths of the light bandsfrom the different light sources are substantially the same. More thantwo light source/photosensor pairs can be used, depending upon therequirements of the measurement application. The detectors in suchembodiments can be, for example, any of the types of photosensors 130described above.

The apparatus 100 can also include at least one temperature sensor 161and/or at least one pressure sensor 162. The temperature and pressuremeasurements provided by these sensors 161, 162 can support furthercorrections to measured attributes, which have been determined fromintensity losses of the first band of light. In some applications, theresults achieved can be affected by temperature and pressure. Whenrequired, compensation can be provided based on information obtainedfrom temperature sensor 161 and/or pressure sensor 162, resulting inmore precise attribute measurement results.

FIG. 2 is a flowchart of an embodiment of a method 200 for measuring aconstituent of a fluid, according to principles of the invention. Themethod 200 may be implemented with, for example, the apparatus 100illustrated in FIG. 1. The method 200 includes selecting a first band oflight for which the constituent has a greater absorption than for asecond band of light (Step 210), sensing the first band of light and thesecond band of light passing along a substantially shared path throughthe fluid (Step 220), and modifying a measured attribute of theconstituent determined from the sensed first band of light in responseto the sensed second band of light to improve the accuracy of themeasured attribute (Step 230).

The fluid can be ozonated water as produced by, for example, an ozonatedwater generator. The constituent can then be ozone. The remainder ofthis description refers to water and ozone as examples of a fluid and aconstituent of a fluid. It will be understood, however, that principlesof the invention may be applied to other fluids and other constituentsof fluids.

The measured attribute of the ozone can be any attribute of interest,for example, a concentration of the ozone. The step of modifying (Step230) can then include correcting the measured concentration for errorsarising from an intensity loss of the sensed first band of lightassociated with one or more factors other than absorption by theconstituent. Such intensity losses may otherwise be misinterpreted asarising from absorption by ozone, and can thus lead to a false increasein measured concentration.

Factors that may cause a decrease in intensity include, for example,bubbles, a reduction in reflectivity of a reflection site of thesubstantially shared path, an impurity in the fluid, and a change in amechanical dimension of a vessel containing the fluid. A decrease inintensity arising from such factors is unrelated to absorption by ozone,but can be falsely interpreted as an increase in absorption by ozonecaused by an increase in ozone concentration. The method 200 can includecausing the ozonated water to flow through a vessel from an ozonatedwater generator to a process tool to permit in situ measurement of theozone concentration (Step 240).

The method 200 can also include alternately directing the first band oflight and the second band of light along the substantially shared path(Step 250). In this case, the first band of light and the second band oflight can then be alternately sensed. The first and second bands oflight can further be alternated with a blank period during whichsubstantially no light is directed along the substantially shared path.For example, during the blank period, the background intensity can beobserved. The background intensity can arise from, for example,photosensor noise and/or light from sources other than a lightintentionally directed along the shared path through the fluid.

The background intensity can increase the apparent sensed intensity ofthe first band of light, causing an error in a concentrationmeasurement. The background measurement can thus permit a furthercorrection to further improve the accuracy of ozone concentrationmeasurements. That is, for example, the measured ozone concentration canbe corrected for background intensity that may falsely decrease theapparent ozone concentration.

The method 200 can include sensing at least one of the first band oflight and the second band of light along at most a portion of thesubstantially shared path, and responsively maintaining an emittedintensity of the first band of light in response to the second band oflight. Thus, for example, as described above, differential aging effectsof LED light sources can be detected. As known to one having skill inthe LED arts, the light intensity output of an LED can decrease withage, for a giving input voltage. Further, different types of LEDs canexhibit different rates of aging.

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. An apparatus for measuring an attribute of ozone in an ozonated liquid, the apparatus comprising: a delivery pipeline to carry the ozonated liquid to a process tool, wherein the delivery pipeline is positioned to permit in situ measurement of the attribute of ozone in the ozonated liquid; a light source that directs a first band of visible light and a second band of visible light through the ozonated liquid in the delivery pipeline, wherein ozone in the ozonated liquid has a greater absorption with the first band of visible light than with the second band of visible light; and a photosensor that senses the first band of visible light and the second band of visible light passing through the ozonated liquid for measuring an attribute of the ozone in the ozonated liquid.
 2. The apparatus of claim 1, wherein the delivery pipeline is positioned to permit full-flow measurement of the attribute in the ozonated liquid.
 3. The apparatus of claim 1, wherein the second band of visible light provides a reference signal to correct measurements derived from the first band of visible light.
 4. The apparatus of claim 1, further comprising a second photosensor positioned to sense the first band of visible light and the second band of visible light passed along a portion of the substantially shared path.
 5. The apparatus of claim 4, wherein the light source includes a first light-emitting diode to generate the first band of light and a second light-emitting diode to generate the second band of light, the second photosensor facilitating detection and correction of differential aging of the first or second light-emitting diodes.
 6. The apparatus of claim 5, wherein the first band of visible light is associated with a yellow-red frequency and a first width, and the second band of visible light is associated with a blue frequency and a second width.
 7. The apparatus of claim 5, wherein the first light-emitting diode comprises a yellow-red light-emitting diode to provide the first band of visible light and the second light-emitting diode comprises a blue light-emitting diode to provide the second band of visible light.
 8. The apparatus of claim 1, wherein the first and second bands of visible light pass through the delivery pipeline along a substantially shared path defined in part by a plurality of reflection sites.
 9. The apparatus of claim 8, wherein the plurality of reflection sites increase a length of the substantially shared path, thereby increasing the measurement sensitivity of the apparatus.
 10. The apparatus of claim 1, wherein the photosensor is positioned along the substantially shared path for sensing the first and second bands of visible light as the first and second bands of visible light pass through the delivery pipeline.
 11. The apparatus of claim 1, further comprising a second photosensor positioned along a longitudinal axis defined by an external surface of the delivery pipeline for sensing the first band of visible light and the second band of visible light passing along the substantially shared path prior to the first and second bands of visible light reaching the photosensor.
 12. The apparatus of claim 1, wherein the delivery pipeline comprises a material that defines an inner surface of the delivery pipeline, the material including a plurality of reflection sites to produce a mirror or diffuse reflection of the first or second bands of visible light.
 13. The apparatus of claim 1, further comprising a coating on an exterior surface of the delivery pipeline to provide a plurality of reflection sites that produce a mirror or diffuse reflection of the first or second bands of visible light.
 14. An ozonated water generator, comprising: a contactor for introducing ozone gas into water to produce ozonated water; a delivery pipeline in fluid communication with the contactor for delivery of ozonated water to a process tool, the delivery pipeline including a plurality of reflection sites that define a path; a light source that directs a first band of visible light and a second band of visible light substantially along the path through the ozonated water in the delivery pipeline, wherein ozone in the ozonated water has a great absorption with the first band of visible light than with the second band of visible light; and a photosensor that senses the first band of visible light and the second band of visible light.
 15. A method for measuring an attribute of ozone in an ozonated liquid, the method comprising: selecting a first band of visible light for which ozone has a greater band of absorption than for a second band of visible light; directing the first and second bands of visible light through a delivery pipeline configured to carry the ozonated liquid to a process tool, the delivery pipeline being positioned to permit in situ measurement of the attribute of ozone in the ozonated liquid; sensing the first and second bands of visible light after the first and second bands of visible blight pass along a substantially shared path through the ozonated liquid; and determining the attribute of the ozone based on the sensed first and second bands of visible light.
 16. The method of claim 15, further comprising correcting for an intensity loss of the sensed first band of visible light associated with at least one factor other than absorption by ozone in the ozonated liquid.
 17. The method of claim 16, wherein the at least one factor comprises at least one of bubbles, a reflectivity of a reflection site of the substantially shared path, an impurity in the ozonated liquid, a mechanical dimension of delivery pipeline containing the ozonated liquid, or any combination thereof.
 18. The method of claim 15, further comprising generating the ozonated liquid in an ozonated liquid generation device.
 19. The method of claim 18, wherein generating the ozonated liquid comprises introducing ozone gas to the liquid using a contactor.
 20. The method of claim 15, further comprising adjusting at least one parameter of an ozonated liquid generation device until the determined attribute of the ozone in the ozonated liquid substantially matches the desired ozone concentration.
 21. The method of claim 15, further comprising alternately directing the first band of visible light and the second band of visible light along the substantially shared path, wherein sensing comprises alternately sensing the first band of visible light and the second band of visible light.
 22. The method of claim 21, wherein alternately directing further comprises alternately directing no light along the substantially shared path.
 23. The method of claim 15, further comprising sensing at least one of the first band of visible light and the second band of visible light after the first and second bands of visible light have passed at most a portion of the substantially shared path, and responsively maintaining an emitted intensity of at least one of the first band of visible light and the second band of visible light.
 24. An apparatus for measuring an attribute of ozone in an ozonated fluid, the apparatus comprising: a vessel to contain the ozonated fluid for delivery to a semiconductor process tool; a light source configured to direct a first band of visible light and a second band of visible light along a substantially shared path though the ozonated fluid in the vessel, the substantially shared path defined in part by a plurality of reflections, wherein the constituent has a greater absorption associated with the first band of visible light than with the second band of visible light; and a photosensor that senses the first band of visible light and the second band of visible light passing along the substantially shared path.
 25. The apparatus of claim 24, wherein the vessel comprises a delivery pipeline for delivering the ozonated fluid to a process tool positioned to permit in situ and near-real-time measurement of the attribute of the ozone in the ozonated fluid.
 26. The apparatus of claim 25, wherein the delivery pipeline is positioned to permit full-flow measurement of the attribute of the ozone in the ozonated fluid. 